With the growing interest in energy conservation, increasingly more industrial work machines are supplied with electric drive assemblies or systems for driving the work machine and operating its various tools or functions. Ongoing developments in electric drive systems have made it possible for electrically driven work machines to effectively match or surpass the performance of predominantly mechanically driven work machines while requiring significantly less fuel and overall energy. As electric drive systems become increasingly more commonplace with respect to industrial work machines, and the like, the demands for more efficient motors and generators and techniques for controlling them have also increased.
A generator of an electric drive machine is typically used to convert mechanical power received from a primary power source, such as a combustion engine, into electrical power for performing one or more operations of the work machine. Additionally, an electric motor may be used to convert electrical power stored within a common bus or storage device into mechanical power. Among the various types of electric motors available for use with an electric drive system, switched reluctance machines have received great interest for being robust, cost-effective, and overall, more efficient. While currently existing systems and methods for controlling switched reluctance machines may provide adequate control, there is still much room for improvement.
For example, square wave input current control profiles are easy to implement and protect the windings of an electric motor from high currents. However, such current control profiles may produce significant variations in torque produced by the electric motor in the course of one rotor cycle, known as torque ripple. Other current profiles may produce a flat torque output with high torque, but may require winding currents that exceed the rated winding current. Producing motors with excessive rating capabilities to accommodate high transient currents is not cost effective.
Control schemes for switched reluctance machines may involve operating two switches of each phase leg of the machine to pulse or chop the electrical current thereby effectively providing a waveform, such as a pulse width modulated (PWM) waveform. U.S. Pat. No. 6,756,757 (the '757 patent) teaches use of a solver to calculate a desired torque profile and uses a lookup table to produce a flat torque output. However, the '757 patent fails to recognize maximum phase current limitations and the effect of limiting phase current on generated torque.
The present disclosure solves one or more of the problems set forth above and/or other problems in the art.